Cutting apparatus and method

ABSTRACT

In a cutting apparatus a rotating carousel conveys caps made of synthetic plastic material to a fixed blade having the shape of a circumferential arc. The caps are rotated about themselves by spindles. The blade cuts an annular weakening line to form the tamperproof ring of the cap. The carousel has an emitter and a laser receiver that cooperate to detect the presence or absence of the cutting edge of the fixed blade. The apparatus ensures good cutting quality.

BACKGROUND OF THE INVENTION

The invention relates to a cutting apparatus and method, in particularfor cutting or engraving plastics or metal (for example aluminium orsteel), more in particular to make a weakening line in caps made ofplastics.

Specifically, but not exclusively, the invention can be used to producecaps made of plastics for closing containers, in particular for makingthe preferential weakening or fracturing line that is used to define atamperproof device intended to indicate the first opening of the cap.

Making the preferential breaking line of a tamperproof ring in caps madeof plastics by cutting apparatuses that comprise a carousel that has aseries of movable spindles that are able to rotate around their axis isknown. In use, the caps to be cut engage in the spindles and are thusrolled on a fixed sector that carries a blade that is suitably shapedaccording to the type of cut that it is desired to perform. The fixedsector can be positioned either outside the carousel that carries thespindles or inside the spindles.

One of the problems of the known apparatuses of this type consists ofthe fact that the cutting blade is subject to wear during use and canaccidentally splinter or break, with consequent deterioration in thequality of the caps produced, such that the correct operation of thetamperproof device is no longer ensured.

This problem is particularly relevant in the case of a machining processthat occurs continuously and in line with other apparatuses.

Solving the above problem by means of periodical checking of the cuttingquality on the caps produced and thus of the correct function of thetamperproof device is known, by removing and checking a sample atperiodical intervals (for example every one or two hours). This solutionnevertheless has the following drawback: for example, if averageproduction speed is 60,000 caps an hour and the sampling period is onehour, if insufficient quality is detected in the sample of caps all the60,000 caps produced in the hour preceding the sampling have to berejected because correct operation of the tamperproof device would notbe guaranteed.

The prior art further comprises U.S. Pat. No. 4,511,054, which disclosesa method and an apparatus to control the quality of the weakening linemade between the tamperproof ring and the ‘skirt’ portion of a cap madeof plastics. U.S. Pat. No. 4,511,054 relates to the problem of improvingand controlling the dimensional tolerances of the weakening lines thatare made on caps made of plastics. The apparatus and the method shown inthis document perform a check directly on each cap. In particular, anoptical apparatus is provided comprising a light source and a detector.During the test, the light source is positioned inside a cap whilst thedetector is positioned outside the cap. The cap is rotated around anaxis thereof whilst a light beam generated by the light source traversesa cap cutting zone and intercepts the detector. Each uncut cap portionis detected through an interruption of the light beam. The opticalapparatus is able to detect whether the cutting zones meet presetdimensional parameters. The use of laser devices for controlling thepositioning and possible damage to or wear of a cutting blade is alsoknown, as is the use of laser devices for controlling the flatness of adisc blade.

The object of European Patent No. EP 1 609 570 is a system forcontrolling the cutting blade, particularly for shearing machines forcutting sheets of paper, plastics, etc. The system has the function ofcontrolling continuously friction wear or overheating deformation of adisc or band blade for cutting the sheet material. The system enablesthe cutting operation to be stopped at the moment in which anoperationally unacceptable blade condition is detected. Measuringsensors (not shown) are provided that detect the variations in theradius of the blade caused by wear. A device is also provided formeasuring the planar deformation of the blade, comprising a distancesensor, for example a laser probe provided with a transmitter/emittercoupled with an optical detector/receiver.

The object of German Patent No. DE 4 232 236 is a device for detectingwithout contact the contour of a tool, such as a knife, a drill, etc.This document discloses the use of a laser device to check the contourof a tool. The device comprises a laser source configured for generatingtwo laser beams, and a detector suitable for receiving the two laserbeams. During operation, the laser beams lick the side surface of thetool and from the manner in which they are intercepted by the detectorthe contour of the tool is detected point by point in space. A devicethat is similar to the one that has just been discussed is also shown inU.S. Pat. No. 4,657,395 and Japanese patent No. JP 62006114.

Japanese patent publication No. JP 54109682 discloses a method and adevice for automatically detecting possible damage to a blade, in whicha laser beam emitted by a light projector hits the surface of the bladeand is reflected at 45 degrees to the hit surface. The reflected beammay or may not be intercepted by the receiver, which produces asignificant signal of the state of damage of the blade. Depending onthis signal, the system is stopped or continues to operate.

U.S. Pat. No. 6,237,455 shows a cutting machine relating to thewoodworking industry, provided with knives and with a detecting devicefor inspecting the knives. In one embodiment (FIGS. 6 and 7) the machinecomprises an annular rotor that supports internally in a cantileveredmanner several knives and through rotational motion drags the knives tocut the pieces of wood. Two sensors are provided that are arranged atopposite ends to the knives and monitor how much the knives projecttowards the longitudinal axis of the annular rotor. The sensors may beproximity sensors. The sensors are arranged in a stationary positionwhilst the knives are moved.

U.S. Pat. No. 6,576,531 discloses a method and an apparatus fordetecting incorrect positioning of a disc blade. A distance sensor, forexample of laser type, is provided, which measures a distance from thedisc blade whilst the latter rotates by detecting the variation of thisdistance, which has to be contained within a given range for correctoperation of the system.

Patent publication WO 2004/004993 shows an apparatus according to thepreamble of the first claim.

SUMMARY OF THE INVENTION

One object of the invention is to provide a cutting apparatus in whichthe good quality of the cutting operation performed is assured.

Another object is to provide a cutting method in which the good qualityof the cut operation is ensured.

One advantage is to make an apparatus and/or a cutting method availablefor making the weakening line in caps made of plastics with relativelyhigh productivity.

Another advantage is to devise an apparatus and/or a cutting method formaking with precision the weakening line in caps made of plastics.

A further advantage is to reduce the risk of rejects in the productionof caps made of plastics provided with a tamperproof device.

These objects and advantages and others again are all reached by theapparatus according to one or more of the claims set out below.

The apparatus in subject may comprise a sensor configured for detectingthe presence/integrity of the cutting edge of the cutting tool thatmakes the weakening line of the tamperproof device in caps made ofplastics for closing containers.

The apparatus in subject may comprise a sensor that is set up fordetecting at least one anomalous operating condition in the cutting tooland which is at least partially moved by a movable element with whichthe apparatus is equipped to give all the caps to be cut a correspondingadvancing movement with respect to the cutting tool.

The aforesaid movable element may comprise a rotating carousel thatcarries a plurality of tools, which in turn rotate with respect to thecarousel, each of which in use is operationally associated with a cap torotate the cap about itself.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood and implemented with reference tothe attached drawings that illustrate some non-limiting embodimentsthereof.

FIG. 1 is a section in a vertical elevation of a part of the apparatus.

FIG. 2 is an enlarged detail of FIG. 1.

FIG. 3 is a top plan view of a part of the apparatus of FIG. 1.

FIG. 4 is an enlarged detail of FIG. 3.

FIG. 5 is a section in vertical elevation of a part of apparatuscomprising the sensor means for detecting faults on the cutting device.

FIG. 6 is an enlarged detail of FIG. 5.

FIG. 7 is a top plan view of the apparatus in FIG. 1 showing the toolsthat rotate the caps to be cut.

FIG. 8 is a top plan view of the apparatus in FIG. 1 showing the fixedparts of the cutting system.

FIG. 9 is an enlarged detail of FIG. 8.

FIG. 10 is a detail of another embodiment of the apparatus.

DETAILED DESCRIPTION

With reference to the aforesaid Figures, 1 shows overall a cuttingapparatus, 2 a cap of plastics for closing containers, 3 a conveyingcarousel, 4 spindles for transmitting rotational motion to the capsbeing machined, 5 a cutting device operationally associated with thecaps, 6 a blade of the aforesaid cutting device, 7 a signals emitter, 8a signals receiver operationally associated with the aforesaid emitter,9 a rotating joint connected to the aforesaid emitter.

The cutting apparatus 1 is used to make a weakening line in a cap madeof plastics to form a tamperproof device (tamperproof ring or band) thatenables the prior opening of the cap to be recognised. In general, theweakening or facilitated fracturing line extends substantiallycircumferally on an annular or skirt portion of the cap, such as todefine a ring-shaped tamperproof device.

The cutting apparatus 1 can be inserted into a complex machining systemwhere the caps may undergo a series of other machinings before and/orafter the cutting operation.

The cap 2 comprises a skirt portion that is the part that is subjectedto cutting to make the weakening line. The cap 2 further comprises abottom portion that closes the skirt portion at a first end. The skirtportion can be threaded internally. The weakening line defines atamperproof ring that is arranged at a second end of the skirt portionopposite the first end.

The carousel 3 is rotated around a (vertical) rotation axis. Thecarousel 3 defines a conveying system that removes the caps 2 from aremoving zone, advances the caps in an orderly manner (one after theother) to a cutting zone, to convey then the cut caps to a release zonewhere it can operate a further conveying system that sends the caps forpossible further machinings.

The carousel 3 defines a circular advancing path (with horizontal plane)for the caps. It is possible to provide other conveying systems that areoptionally able to define other advancing paths.

The carousel 3 has a plurality of spindles 4 that are distributed on thecarousel angularly spaced apart from one another, for exampleequidistant. In the specific case, there are six spindles, but it isalso possible to provide a number that is greater or less than six.

Each spindle 4 is provided with the possibility of rotating around arotation axis thereof with respect to the carousel 3. The rotation axisof each spindle 4 can be, as in the specific case, vertical. Therotation axis of each spindle 4 can be, as in the specific case,parallel to the rotation axis of the carousel 3. The rotation axes ofthe spindles 4 can be, as in the specific case, parallel to one another.

The spindles 4 movement system is of known type and does not thereforerequire further explanations.

In use, as known, each spindle 4 is inserted inside a corresponding cap2. The caps 2 can be arranged, as in the specific case, with the bottomportion facing downwards. In this case the spindle 4 enters the cap 2from above.

It is possible to use other systems for transmitting cutting motion tothe caps 2, for example configured for conveying the caps 2 with adifferent orientation thereof (for example with the bottom portionfacing upwards, or oriented vertically, or obliquely, or with variableorientation along the path).

The cutting device 5 comprises a supporting unit that retains in aworking position, which in the specific case is fixed, the blade 6 thatforms the weakening line on the various caps 2 conveyed by thespindle-carrying carousel. The blade 6 can be, as in the specific case,substantially in the shape of a circular sector. The blade 6 can beprovided, as in the specific case, with a blade with an arched shape. Inparticular, the blade 6 can be provided, as in the specific case, with ablade with substantially the shape of a circumference arc. The bladewith an arched shape can be extended, as in the specific case, by anangle of approximately 38-39 degrees, for example comprised between 30and 45 degrees. It is nevertheless possible to provide an angular extentthat is less than 30 degrees or greater than 45 degrees.

The cutting device 5 is set up for operating along the advancing path ofthe caps 2. This advancing path is the one defined by the conveyingmeans of the caps with which the apparatus is provided and which in thespecific case comprises the carousel 3 that, as is seen, defines atleast one portion of advancing path in the shape of a circumference arcthat substantially corresponds to the shape of the cutting edge. Eachspindle 4 then defines a rotation motion of the corresponding cap aboutitself to enable the blade 6 to operate in a circumferential directionon the skirt portion of the cap for a desired angular size, if necessaryto obtain a weakening line extending 360° over an entire circumference.In use, each spindle 4 will force the corresponding cap to roll on theblade 6 so as to cut the cap at 360°.

The blade 6 may comprise, as in the specific case, a cutting edge thatis continuous or configured to make a continuous weakening line. It ispossible to provide a blade provided with a discontinuous cutting edgeor which is configured to make a discontinuous weakening line, forexample a line comprising a series of bridges intended for fracturingand which are interrupted by a series of windows.

The apparatus 1 is further provided with sensor means configured fordetecting a fault (for example wear, shifting from the desired position,breakage or removal of parts, etc) in the cutting device, in particularin the blade 6 of the device.

The sensor means can be configured, as in the specific case, fordetecting the presence or absence of the cutting edge along the entireor at least part of the extent of the cutting blade 6.

The sensor means can comprise at least one presence sensor that is ableto detect the presence or absence (or shift from a desired position) ofat least one part of the cutting device 5, in particular the presence orabsence (or the shift from a desired position) of an operating part ofthe cutting device, such as, for example, the presence or absence (orshift from a desired position) of at least one part of a cutting edgewith which the cutting device 5 is provided.

The sensor means can comprise, as in the specific case, a laser sensor.The sensor means can comprise, as in the specific case, an emitter 7 ofsignals and a corresponding receiver 8 of the signals emitted by thereceiver 7. The sensor means can comprise, as in the specific case, aradiation emitting sensor (for example of optical type) that is set upin such a way that at least one part of the emitted radiation affects atleast one part of the blade 6 of the cutting device 5.

The radiation emitting sensor (in the specific example of laser type)may have, as in the specific example, a measuring size comprised between1 mm and 15 mm. The measuring size, which, as known, influences readingresolution, can be for example 5 mm. The measuring size may consist, asin the specific case, of the diameter of the circular radiation beamsemitted.

The emitter 7 and/or the receiver 8 can be associated or applied, forexample firmly mounted as in the specific case, to the conveying systemthat supplies to the caps 2 the advancing motion to the cutting device 5and/or the cutting motion proper. The emitter 7 and/or the receiver 8can be associated or applied, for example integrally mounted as in thespecific case, on the carousel 3 that carries the spindles 4.

The receiver 8 can be positioned, as in the specific case, opposite theemitter 7 at a preset distance therefrom and remain in the samecorresponding position in relation to the emitter 7 during movement ofthe conveying system of the caps 2. The position of the emitter 7 and ofthe receiver 8 will be able to enable the control (laser) radiation beamto reach at least partially the cutting blade 6.

The emitter 7 and the receiver 8 are arranged spaced apart from oneanother (for example along a vertical direction as in the illustratedexample) in such a way that the blade 6 is interposed between theemitter 7 and the receiver 8 for at least a portion of the pathtravelled by the emitter 7 and by the receiver 8. The latter, i.e.rotated by the carousel 3, are arranged in such a manner that for aportion of this rotation the radiation beam affects the blade 6. Inparticular, the radiation beam moves in such a manner as to affect theentire length of the blade 6.

The sensor means can then be connected, as in the specific case, to amonitoring and/or control unit that will process the received signal todetect the fault condition or correct operation of the apparatus.

The connection of the sensor means with the monitoring and/or controlunit can be, as in the specific case, an electric connection through arotating joint 9, or a wireless connection (for example radio waves, orinfrared waves, or laser), or yet another type of connection.

In use, the radiation beam emitted by the emitter 7 (and received by theopposite receiver 8) can meet the cutting device 5 at each revolution ofthe carousel 3.

The carousel 3 conveys the various caps 2 in an orderly manner (oneafter the other) to the cutting device 5 and further conveys the sensormeans (the emitter 7 and the receiver 8) to perform a rotational motionby periodically passing near the blade 6. The various caps 2 are furtherprovided with a further rotating (cutting) motion about itself by thespindles 4.

It is possible to provide, as in the specific case, for themonitoring/control unit being able to activate the sensor means (beingable, in particular, to emit the radiation beam for reading theconditions of the blade 6) at least, or only, at the cutting blade 6, inparticular when, during the rotation of the carousel 3, the emitter 7passes in front of the blade 6 for the size of the arc (circumference)extent of the blade, i.e. in the specific case for an arc of 38°-39°.

In operation, at each revolution of the carousel 3 the sensor means(emitter 7 and receiver 8 cooperating together) will detect the presenceof the cutting edge of the blade 6 and will indicate a fault condition(with possible automatic stop of the apparatus) if, for example, aportion of cutting edge should be missing along the extent of the blade6, or if, for example, the cutting edge were diminished with respect toan initial position (initial position that can be stored by themonitoring/control unit in an initial operating step).

Precision in reading the condition of the cutting device 5 depends onvarious factors, including the stiffness of the apparatus overall and inparticular of the apparatus parts on which the sensor means is applied,and the absence or the size of the clearance between the reciprocallymoving parts (in particular between the elements that rotate), etc.

The fact of having at least a part of the sensor means associated withat least one apparatus part that is substantially integral with the caps(i.e. a movable apparatus part that moves the caps), enables thepresence of an anomalous situation (incorrect cutting) to be detectedthat is due, for example, to an undesired or uncontrolled change to thepath of the caps 2 conveyed by the carousel 3. In fact, taking as anexample the specific case illustrated here, as the sensor means is atleast in part integral in motion with the caps, the variation of thetrajectory of the caps will also entail a variation in the trajectory ofthe sensor means and thus the report of a shift (both of the sensormeans and of the caps) relative with respect to the cutting means.

Thus, the fact of having at least one part of the sensor meansassociated with at least one apparatus part substantially integral withthe caps (i.e. a movable apparatus part that moves the caps), ensuresthat a fault situation will be reported that is due to even a slightshift in the mutual positioning between the apparatus parts that are inreciprocal movement (such as, for example, the part that issubstantially integral with the cutting device and the part that issubstantially integral with the caps), with respect to a nominal orreference positioning.

In the embodiment illustrated in FIG. 10, the apparatus substantiallyconforms to that of FIGS. 1 to 9. The apparatus in FIG. 10 has areference element, indicated by 10, which is set up in a zone of thepath along which the sensor (emitter 7 and receiver 8 unit) travels. Thereference element 10 can be fixed. The reference element 10 can bearranged in such a way as to be integral, or stationary, with respect tothe cutting device 5 in order to simulate the presence thereof inanother portion of the advancing path of the conveying system (carousel3) of the caps and of the sensor (or sensors). The elements in FIG. 10that are similar to those in FIGS. 1 to 9 have been indicated by thesame numbering.

The reference element 10 can be configured in such a manner as toreproduce or at least simulate the presence of a cutting device (inparticular of a cutting blade) that is effectively operational like thecutting device 5. The reference element 10 may have, for example, aconformation that is similar to that of the blade 6. The referenceelement 10 may comprise, for example, a body that reproduces at leastpartially the configuration of the blade 6 which is effectivelyoperational and which is arranged at the same radial distance that theblade 6 has from the rotation axis of the carousel 3.

The reference element 10 can be situated in a zone of the path travelledby the sensor that is far from the actual cutting zone (where the blade6 is present). The reference element 10 can be situated, for example, ina non-operating zone where cutting of the caps is not provided and wherethe passage of the caps may not be provided for either. The referenceelement 10 can be situated, for example, in a zone of the circular pathof the sensor that is diametrically opposite the operating zone wherethe cutting device 5 operates.

In use, the sensor (emitter 7 and receiver 8 unit), which is active onthe cutting device 5, is also activated in a path zone where thereference element 10 is present. Activation and the manner of operationof the sensor (such as the corresponding arrangement of the variousparts of the sensor with respect to the object to be detected on whichthe sensor operates) occur in a similar manner to what was disclosedbefore. The sensor, being operationally associated also with thereference element 10, can provide an indirect indication of possiblefaults in the operation of the apparatus, for example in the cuttingoperation. The sensor may, for example, detect an undesired movement ofthe position of the conveying system (carousel) of the caps such as tocause an incorrect variation in the advancing path of the caps. Thereference element 10 can also be used to check correct operation of thesensor.

The sensor is configured so as to detect the position of the referenceelement 10 and to send a corresponding signal to the monitoring and/orcontrol unit. The latter can compare the signal received, indicating theactual position of the reference element (position with respect to thesensor), with a signal indicating the desired preset position. If theshift from the desired position exceeds a set threshold, the monitoringand control unit will intervene appropriately (by reporting and/orstopping the apparatus).

Detection of shift from a normal situation (for example shift beyond agiven threshold) indicates incorrect operation of the sensor and/or afault in the conveying system (of the sensor and of the caps).

In one embodiment, it is possible to activate the sensor only on thereference element 10, in this case the sensor might not be configuredfor operating on the cutting device 5.

It is possible to configure the monitoring and/or control unit in such amanner as to program detecting of the sensor means only in set zones ofthe path of the sensor means in such a way that, in the case of adiscontinuous blade, it is possible to detect the presence of a cuttingedge provided with preset interruptions (notches).

In other embodiments, it is possible to provide for at least one part ofthe cutting motion being supplied also, or only, to the cutting means(blade) rather than, as in the specific case, only to the caps. Also inthis case the sensor means can be associated (in part) with the cuttingmeans and/or (in part) with the caps.

In other embodiments, it is possible to set up the cutting means in sucha manner that it operates inside the rotational or at least curved pathof the caps, rather than outside as in the illustrated example. In stillother embodiments it is possible to provide for at least one part of thepath of the caps in the cutting zone being substantially rectilinear.

In other embodiments, it is possible to associate the sensor meansoperationally only with the cutting means, without thus applying atleast a part of the sensor means to the apparatus part that carries thecaps.

In other embodiments, it is possible to set up a plurality of sensormeans. For example, two or more radiation emitter/receiver unitsarranged spaced apart from one another can be associated with themovable part of the cutting apparatus. The various sensor means could,for example, be located on a carousel which rotates on a samecircumference which is co-axial with the rotation axis of the carouseland be angularly equidistant from one another.

The apparatus disclosed above may thus comprise a control system forcontrolling the blade that forms the weakening line in caps made ofplastics. This control system may comprise in turn at least one sensorthat is suitable for detecting the presence of the cutting edge of theblade. The sensor can be set up to operate with a frequency that dependson the frequency with which the blade performs the cut on the caps. Inparticular, the sensor can be set up to operate at each revolution thata rotating carousel performs that conveys the caps and confers theretoat least a part of the cutting motion.

As in the specific illustrated example, the maximum number of caps thatcan be produced with an incorrect cut (i.e. the maximum number ofrejected caps) cannot exceed the number of caps carried simultaneouslyby the conveying carousel, and cannot exceed the number of spindles 4contained in the carousel 3 (a number that is normally the same as six,twelve, or twenty-four).

As mentioned, it is possible to set up also two or more control sensorsfor controlling correct operation of the apparatus. In particular, it ispossible to set up a sensor or group of sensors (for example emitter andreceiver) for each spindle, i.e. a number of sensors that is the same asthe number of spindles.

All the various embodiments disclosed above can be combined together inany possible combination of elements.

1-13. (canceled)
 14. An apparatus comprising: a cutting deviceconfigured for forming at least one weakening zone on at least one cap;a conveying device for supplying said cutting device with said at leastone cap, said conveying device comprising at least one movablesupporting element which carries said at least one cap; wherein theapparatus comprises at least one sensor which is able to detect at leastone faulty operating condition of a cutting device, said at least onesensor being arranged for operating on said cutting device, at least apart of said sensor being carried by said movable supporting element,wherein said at least one sensor comprises a presence sensor that isable to detect the presence, or the absence, or the deviation from adesired position, of at least a part of a cutting edge with which saidcutting device is provided.
 15. An apparatus according to claim 14,wherein said at least one sensor is configured for detecting a positionof at least a part of said cutting device, whereby a deviation from adesired relative position of said at least a part of said cutting devicewith respect to said movable supporting element is determinable.
 16. Anapparatus according to claim 15, comprising a reference element arrangedin a preset position along an advancing path of said movable supportingelement, said at least one sensor being configured for detecting aposition of at least a part of said reference element, whereby adeviation from a desired relative position of said at least a part ofsaid reference element with respect to said movable supporting elementis determinable.
 17. An apparatus according to claim 14, wherein saidsensor comprises at least an emitter of signals and at least a receiverof signals each cooperating with the other, said emitter and saidreceiver being carried by said movable supporting element.
 18. Anapparatus according to claim 17, wherein said sensor is configured toassume at least an operating configuration in which at least a part of ablade of said cutting device operating on the cap is interposed betweensaid emitter and said receiver.
 19. An apparatus according to claim 14,wherein said conveying device comprises at least one rotating carouselthat has a plurality of spindles on a peripheral zone thereof, eachspindle of said plurality of spindles rotating in turn with respect tothe carousel and being configured for engaging with a cap such as torotate the cap, said cutting device comprising a fixed blade having acutting edge extending at least partially along a circumferential arc,said sensor being operationally associated with said cutting edge. 20.An apparatus according to claim 14, wherein at least a part of saidsensor is movable with the possibility of performing a motion along aclosed-loop path arranged such that said at least a part of said sensoris periodically operational with respect to, for example facing or near,at least a part of said cutting device.
 21. An apparatus according toclaim 20, wherein said sensor is connected to a control deviceconfigured for periodically activating said sensor when said movablepart of said sensor is operational with respect to, for example facingor near, said at least a part of said cutting device.
 22. An apparatusaccording to claim 14, wherein said at least a sensor comprises aradiation emitting sensor that is able to emit radiation, said radiationemitting sensor being arranged such that said emitted radiation at leastpartially affects said cutting device.
 23. A method for cutting a cap,comprising the steps of: supplying at least a cap to a cutting device;forming at least a weakening zone on said at least a cap by said cuttingdevice; detecting by a sensor whether said cutting device has a faultyoperating condition or not, wherein said detecting step comprisesdetecting the presence, or absence, or the deviation from a desiredposition, of at least a part of a cutting edge with which is providedsaid cutting device; and providing a movable supporting element thatcarries said at least a cap and at least a part of said sensor to saidcutting device.
 24. A method according to claim 23, wherein saiddetecting step comprises emitting radiation that at least partiallyaffects said cutting device.
 25. A method according to claim 23, whereinsaid movable supporting element carries said at least a cap and anemitter and a receiver each cooperating with the other to emit/receive aradiation beam, said supporting element being moved such that saidradiation beam hits said cutting device.
 26. A method according to claim23, and further comprising the step of moving at least a part of saidsensor along a closed-loop path arranged such that said at least a partof said sensor periodically faces at least a part of said cuttingdevice, said movable part of said sensor being periodically activatedwhen it faces said at least a part of said cutting device.